#define  _CRT_SECURE_NO_WARNINGS 1
typedef struct ListNode ListNode;

bool hasCycle(struct ListNode* head) {
    ListNode* fast = head, * slow = head;
    while (fast && fast->next) {

        fast = fast->next->next;
        slow = slow->next;
        if (fast == slow) {
            return true;
        }

    }
    return false;
}